The present disclosure relates to technologies for reducing memory access in devices for drawing and displaying images.
In recent years, computer graphics have been widely used in user interfaces for mobile telephones or digital televisions, and systems for producing images for video games, in order to allow for man-machine interactive operation, resulting in improved user experience. On the other hand, as technologies have been developed, display devices used in apparatuses have had higher definition, and therefore, there has been a demand for an image drawing/displaying device having higher performance. The frequency of memory access for drawing or displaying has increased, resulting in an increase in power consumption.
To address this, a technique has been proposed in which when a first image and a second image which are stored in a memory are displayed with the second image being superimposed on the first image, a start line number of a portion in which the second image is to be displayed, and the number of lines to be displayed, are calculated, and when a line in the second image contains only transparent pixels, only the first image in the memory is accessed for that line, whereby useless memory access is reduced (see Japanese Unexamined Patent Publication No. 2003-288067).
Also, when a graphic is drawn as the second image, a draw range in the horizontal direction is calculated, a desired range on each line is determined to be a superimposition display region, and for the other portion, only the first image in the memory is accessed, whereby useless memory access is reduced (see Japanese Unexamined Patent Publication No. 2004-166017).
However, in the above conventional techniques, it is assumed that images to be superimposed together are rectangular. The above conventional techniques cannot be easily applied to superimposition of graphics having any arbitrary shapes, such as computer graphics. In addition, a counter or a comparator is required for each of images to be superimposed together. Therefore, the above conventional techniques cannot be practically applied to tens of thousands of computer graphics which are typically displayed at once.
For example, when ten thousand images are processed using the technique described in Japanese Unexamined Patent Publication No. 2003-288067 above, ten thousand comparators for comparing the line number of each line and the start line number of each image, and ten thousand counters for counting down the lines to the end of memory access to each image, are required, which is not practically feasible.